To secure safety of an apparatus, equipment, and a structure, such as an iron bridge or concrete structure, it is necessary to grasp the states, such as stress, strain and deformation from the design phase to the in-service phase. For example, hard and fragile materials, such as concrete or ceramics, unlike an elastoplastic material like a metal material, have a small deformation range until cracking, which is a phenomenon of a “minute strain area” of several hundred micro stain order, thus requiring a relatively high-precision measurement. Conventionally, the main stream of the method of measuring stress, strain and deformation is local measurement using a strain gauge. A strain gauge is configured to have a thin metal wire to be a resistor disposed in a folded state in an insulating film. The strain gauge is adhered to the top surface an object to be measured, and stretches or shrinks according to the stress, strain, and deformation of the to-be-measured object, so that the stress, strain, deformation and the like of the to-be-measured object is measured from a change in the resistance of the thin metal wire to be a resistor.
Multiple measuring methods of measuring the amount of displacement (deformation) or strain through image processing have been proposed recently as other measuring methods. There is a digital image correlation method as a method of simultaneously acquiring the amount of deformation and the direction thereof using a digital image picked up by a CCD camera or the like.
There are Patent Literature 1 and Non-patent Literature 1 as references on the related art. Patent Literature 1 discloses a technique on a 90-degree image rotating method and apparatus for fast rotating input digital image data by 90 degrees and outputting the image data. Non-patent Literature 1 discloses the principle and application of the digital image correlation method.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. H8-63593    Non-patent Literature 1: “Digital Speckle Pattern Interferometry and Related Techniques” edited by Pramod K. Rastogi (UK), John Wiley & Sons, Ltd. Press, 2001